This research will examine how "molecular" (small-scale) variables affect choice behavior. One major variable to be investigated will be delay of reinforcement, and its role in "self- control" choices (where a subject must choose between a small, immediate reinforcer and a larger but delayed reinforcer). Choice behavior will also be studied in situations where the alternatives include one certain reinforcer and one probabilistic reinforcer. The subjects in this research will be pigeons performing in standard operant conditioning chambers, and two main procedures will be used to study preference. One is an adjusting-delay procedure developed by the PI, in which the choice period is brief--a subject chooses between two alternatives by making a single response. The other is the more widely used concurrent-chains procedure, which involves choice periods of more extended durations, and in which the measure of preference is the proportion of responses allocated to each alternative. One goal of this research will be to apply the PI's theory of choice to the complex yet orderly patterns of behavior that are found when extended choice periods are used. Many of the proposed experiments are designed to distinguish between the PI's theory and other theories of choice. These theories differ along several dimensions, such as their treatment of reinforcement rate, conditioned reinforcement, and probabilistic reinforcement. The proposed experiments should help to decide which of these theoretical alternatives are viable and which are not. Many important everyday choices involve a conflict between an individual's short-term and long-term interests (e.g., the pleasures of smoking, drinking, or overeating versus future health). For this reason, it seems appropriate to submit this proposal, which is directed toward developing a better understanding of the effects of delayed and uncertain reinforcers, to NIMH.